Redox treatment of alunite ore

ABSTRACT

This invention relates to a method for recovering aluminum hydroxide from alunite ore by roasting the ore to remove water of hydration, roasting it again in a reducing atmosphere to remove sulfate, roasting a third time in an oxidizing atmosphere to convert any sulfides formed in the second roast, leaching with water to remove potassium and sulfate, extracting the aluminum content with a mixture of sodium hydroxide and potassium hydroxide, removing contaminant silica from the leach solution, and precipitating aluminum hydroxide by cooling and seeding the solution.

O United States Patent 1191 1111 3,890,425 Stevens et a]. 1 June 17,1975 [5 REDOX TREATMENT OF ALUNITE ORE 1,189,254 7/1916 Hershman et al423/120 l,l9l,l05 7/l9l6 Hershman 423/l22 [75] Inventors: DouglasStevens, Golden, Colo.; l 195 655 8/1916 Cha 423 ppe /l3l s f aOwensboro, Y 2,120,840 6/1938 McCullough 423/127 Larry D. Jennmgs,Arvada. Cold; 2,398,425 4/1946 Haff 4231120 Frank M. Stephens, ,lr.,Lakewood, 3,652,208 3/1972 Burk et al 423/127 Colo.; Francis J. Bowen,Golden, Colo.; David L. Thompson; Julian V. Copenhaver, Jr., both ofArvada, Primary ExaminerHerbert T. Carter Colo. Attorney, Agent, orFirm-Van C. Wilks; Herbert M. [731 Assignees: Southwire Company,Carrollton, Hanegan; Stanley Tate (3a.; National Steel Corporation,Pittsburgh, Pa.; Earth Sciences, Inc., GOidCl'l, COiO- [22] Filed: Mar.21, 1974 This invention relates to a method for recovering alu- [211App]' 453234 minum hydroxide from alunite ore by roasting the ore toremove water of hydration, roasting it again in a re- [52] US. Cl.4231127; 423/1 l 1; 423/118; ducing atmosphere to remove sulfate,roasting a third 423/120; 423/l3l; 423/629; 423/339; time in anoxidizing atmosphere to convert any sul- 423/567; 423/530; 423/l22 fidesformed in the second roast, leaching with water [51] int. Cl C0lf 7/06;COlf 7/02 to remove potassium and sulfate, extracting the alumil Fieldof Search 423/1 l 1 num content with a mixture of sodium hydroxide and423/131, 629, 122; 75/97 R, 101 R potassium hydroxide, removingcontaminant silica from the leach solution, and precipitating aluminum[56] References Cited hydroxide by cooling and seeding the solution.

UNITED STATES PATENTS 1 1,070,324 8/1913 Chappell 423/131 15 Claims, 2Drawing Figures sum/a SULFUR wars/1 or won/man 010x105 0x105 ALUNITE 1mm1/ a one +1 msnii2 E s'iiii :322:12 s no cAnaou mmoxws,

HYDROGEN DIGEST/0N DESILICATM 1- warm/mm AL (OH) 3 PATENTEDJUN 1 7 1915SEE? Gamma 530E ZQEUIGNS Allll Til.

REDOX TREATMENT OF ALUNITE ORE FIELD OF THE INVENTION The presentinvention concerns a method for recovering aluminum hydroxide from orecontaining alunite by calcination, roasting the calcined ore in areducing atmosphere, further roasting the reduced ore in an oxidizingatomsphere, leaching with water and subsequent digestion of the solidsresulting from the water leach with a mixture of alkali metalhydroxides.

DESCRIPTION OF THE PRIOR ART Various techniques have been proposed forrecovering alumina from ore containing alunite. Of the varioustechniques disclosed by the prior art the general method involvestreating alunite ore with concentrated sulfuric acid following byroasting or vice versa, with 80;, recovered as a bi-product andsubsequently converted into sulfuric acid and reused in the process, thealuminum being retained in solution as a sulfate. Potash (K is thenadded at a pH of between I and 2 to precipitate alum [K,SO .Al (SO .l8HO]. After precipitation the alum is then roasted to disassociate thealuminum sulfate, with the production of S0 and aluminum oxide which arethen recovered by crystallization. Ordinarily the prior art practionershave used much effort and expense to eliminate potash. US. Pat. No.1,948,887 (Saunders) is representative of the prior art techniques. US.Pat. No. 1,406,890 (Pedersen) further discloses the precipitation ofpotash alumn by the addition of potassium sulfate to an acidic leachsolution. Loevenstein, US. Pat. No. 2,958,580, teaches the recovery ofaluminum as aluminum sulfate by digesting aluminum ore with sulfuricacid.

Although each of the aforementioned techniques may be useful for theparticular application referred to, none of these conventionaltechniques is suitable for recovering aluminum hydroxide from a lowgrade aluminum ore containing alunite, which consists of aluminum,potassium, sodium, sulfate and water. Such ore being domestic to theUnited States in large quantities offers a relatively untouched sourceof aluminum.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide a method for overcoming the aforementioneddisadvantages of the prior art techniques for recovering aluminumhydroxide from ore containing alunite.

It is a further object of the present invention to provide a novelmethod for economically extracting aluminum hydroxide from orecontaining alunite.

Another object of this invention is to provide a novel and economicalmethod for separating aluminum hydroxide and other valuable componentsfrom ore containing alunite, which consists of aluminum, potassium,sodium, sulfate and water.

This and other objects, features and advantages of the present inventionwill be apparent from the following description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a general diagramaticrepresentation of an embodiment of this invention.

FIG. 2 is a diagramatic representation of an embodiment of thisinvention depicting an optional method of silica removal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, which is ageneral diagramatic flow sheet of an embodiment of this invention, orecontaining what is commonly known as alunite, which has an approximateempirical formula of [K Al (OH)|2. (SO,) [Na Al (OH), (50 and orcombinations thereof, is roasted to remove the water of hydration,roasted again in a reducing atmosphere to liberate a portion of thesulfate present as S0,, roasted a third time in an oxidizing atmosphereto convert any sulfides formed in the reduction roast, and leached withwater and the liquid and solid portions of the resultant slurry areseparated. The solid component is then digested with a mixture of alkalimetal hydroxides and the liquid and solid portions are separated in asecond separation step. The liquid portion is heated and/or seeded toremove silica by precipitating sodium aluminum silicate, the remainingliquid is then cooled and/or seeded to precipitate and recover aluminumhydroxide.

Advantageously, the ore containing alunite is roasted in thedehydration, reduction and oxidation steps at a temperature of fromabout 400C to about 850C to effect the removal of the water of hydrationand sulfates existing as A1 (SO4)a. Preferably the ore is roasted in thedehydration, reduction and oxidation steps at a temperature of fromabout 500C to about 650C. Advantageously, the roasting steps are carriedout at atmospheric pressure in fluidized-bed reactors, rotating kilns orthe like, and the preferred temperatures maintained for from aboutone-half minute to about six hours in each step. The residence timewithin each step varying greatly depending upon the type equipment used.

The reducing atmosphere in the reduction roast can be reducing gasessuch as hydrogen, hydrocarbons, carbon monoxide. or mixtures thereof.The sulfur dioxide emitted from the reduction roast can then beconverted to commercial products such as elemental sulfur, sulfuric acidand the like.

The oxidizing atmosphere of the oxidation roast can be air, oxygen ormixtures of air and other oxidizing gases. The sulfur oxides emittedfrom the oxidation roast can also be converted to commercial productssuch as elemental sulfur, sulfuric acid and the like.

The roasted ore is then leached with a solvent, preferably water or analkaline solution. The liquid and solid portions of the resultant slurryare then separated in a first separation step by conventional means suchas thickener tanks, filters, belt extractor filters and the like.

The solid portion therein separated is then digested with a mixture ofalkali metal hydroxides having a concentration of up to about 300 gramsper liter caustic expressed as Na,CO Preferably the alkali metalhydroxides used are sodium hydroxide and potassium hydroxide.Advantageously, the digestion conditions are: atmospheric pressure, atemperature of from about C to about I 10C and a digestion time of fromabout five minutes to about two hours.

The digestion product is then separated in a second separation step byconventional means such as thickener tanks, filters and the like. Theseparated liquid portion is then treated to remove excess silica byheating and/or seeding with sodium aluminum silicates. Advantageouslyaggitation is applied to this liquid portion during the removal ofexcess silica. lf heating at atmospheric pressure is used in this step,a temperature of about 90C for at least one hour is required. If heatingwith pressure in excess of one atmosphere is used, a temperature of fromabout 90C to about 200C for at least fifteen minutes is required.Advantageously the heating is carried out at a pressure of from about0.5 atmosphere to about 7 atmospheres for a time of at least fifteenminutes.

After removal of silica. which is precipitated as sodium aluminumsilicate, the resultant liquid is cooled to precipitate crystallinealuminum hydroxide, which is then separated from the liquid.Advantageously the liquid is seeded with aluminum hydroxide crystalsduring the cooling step to accelerate the rate of precipitation and tocontrol the particle size of crystalline aluminum hydroxide.

The liquid from the first separation step may be processed by vacuum orcooling crystallization to precipitate potassium sulfate.

The following specific example is intended to be illustrative of theinvention herein described, but not limit ing of the scope thereof.

EXAMPLE I A charge of alunite ore weighing about 200 grams was placed ina Vycor retort. The retort was then placed in a preheated electricfurnace, the furnace lid was closed and the temperature raised to about580 to about 600C and held at this level for about 60 minutes. Duringroasting, the retort was rotated continuously at about one rpm andevolved gases were swept from the retort by a stream of air.

After roasting under the conditions recited above the ore was roastedfor about 30 minutes at a temperature of about 580C in an atmosphereconsisting of 50 percent hydrogen gas and 50 percent carbon monoxidegas. At the conclusion of this roast in a reducing atmosphere theroasting chamber was purged with nitrogen and the ore roasted for about30 minutes in an air at mosphere.

The roasted ore was then ground to 35 mesh and mixed with water at a 25percent solids level and the slurry was heated to between 75 and 80C andmechanically agitated while being held at this temperature for one hour.

After separation of the liquid and solid portions of the water leachslurry the solid portion thereof was digested in a caustic solutioncomprising essentially sodium and potassium hydroxides having a causticconcentration of about 220 grams per liter as Na CO The slurry wasboiled at a pressure of one atmosphere with mechanical agitation for onehour and the liquid and solid portions thereof separated.

The digestion liquor was then introduced into a precipitation assemblyconsisting of one liter graduated cylinders equipped with paddles tostir the liquid from top to bottom. The precipitations were maintainedat a constant temperature of 55C and rotated constantly at 125 to 150rmp and stirred just enough to prevent settling. After introduction ofthe digestion liquor into the precipitation apparatus and stirring wasstarted, 20 grams of wet seed gm A1 0 dry) were introduced in smallportions until all seed material had been added. Precipitation was thenallowed to proceed with constant stirring. At the termination of thetest 52 percent of the extracted alumina had been precipitated and wascalcined at l000C.

This invention has been described in detail with par ticular referenceto preferred embodiments thereof. it should be understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described hereinbefore and as defined in theappended claims.

What is claimed is:

l. A method for recovering aluminum hydroxide and other valuableconstituents from ore containing alunite, comprising the steps of:

a. roasting the ore to remove water of hydration,

b. roasting the dehydrated ore resulting from Step (a) in a reducingatmosphere to remove sulfate,

c. roasting the reduced ore resulting from Step (b) in an oxidizingatmosphere to convert sulfides to sulfur oxides,

d. leaching the oxidized ore resulting from Step (c) with solvent toremove potassium and sulfate,

e. separating the liquid and solid portions of the slurry resulting fromStep (d),

f. digesting the solid portion resulting from Step (e) with an aqueousmixture of alkali metal hydroxides at a concentration and at atemperature sufficient to extract the aluminum content from said solidportion,

g. separating the liquid and solid portions of the digestion mixtureresulting from Step (f),

h. precipitating silica from the liquid portion resulting from Step (g),

i. separating the supernatant from the precipitant resulting from Step(h),

j. precipitating aluminum hydroxide from the supernatant resulting fromStep (i) and k. separating the supernatant from the precipitatedaluminum hydroxide resulting from Step (j).

2. The method of claim 1 in which Step (a), Step (b) and Step (c) arecarried out at a temperature of from about 400C to about 850C for a timeof from about one-half minute to about six hours for each step.

3. The method of claim 1 in which Step (a), Step (b) and Step (c) arecarried out at a temperature of from about 500C to about 650C for a timeof from about one-half minute to about six hours for each step.

4. The method of claim 1 wherein the reducing atmosphere of Step (b) isselected from the group consisting hydrogen, hydrocarbons, carbonmonoxide and mixtures thereof.

5. The method of claim 1 wherein the oxidizing atmosphere of Step (c) isselected from the group consisting of air, oxygen and mixtures thereof.

6. The method of claim 1 wherein the solvent of Step ((1) is selectedfrom the group consisting of water and alkaline solutions.

7. The method ofclaim 1 wherein the alkali metal hydroxides of Step (f)are selected from the group consisting of sodium hydroxide and potassiumhydroxide.

8. The method of claim 1 in which the precipitation of silica of Step(h) is carried out by heating the liquid to a temperature of about C forat least one hour at atmospheric pressure.

9. The method of claim 1 in which the precipitation of silica of Step(h) is carried out by heating the liquid at a pressure of from about 0.5atmospheres to about 7 atmospheres at a temperature of from about 90C toabout 200C for at least fifteen minutes.

13. The method of claim 1 containing the additional step ofprecipitating potassium sulfate from the liquid resulting from Step (e).

14. The method of claim 1 containing the additional step of convertingthe sulfate removed in Step (b) into sulfuric acid.

15. The method of claim 1 containing the additional step of convertingthe sulfate removed in Step (b) into elemental sulfur.

1. A METHOD FOR RECOVERING ALUMINUM HYDROXIDE AND OTHER VALUABLECONSTITUENTS FROM ORE CONTAINING ALUNITE, COMPRISING THE STEPS OF: A.ROASTING THE ORE TO REMOVE WATER BY HYDRATION, B. ROASTING THEDEHYDRATED ORE RESULTING FROM STEP (A) IN A REDUCING ATMOSPHERE TOREMOVE SULFATE, C. ROASTING THE REDUCED ORE RESULTING FROM STEP (B) INAN OXIDIZING ATMOSPHERE TO CONVERT SULFIDES TO SULFUR OXIDES, D.LEACHING THE OXIDIZED ORE RESULTING FROM STEP (C) WITH SOLVENT TO REMOVEPOTASSIUM AND SULFATE, E. SEPARATING THE LIQUID AND SOLID PORTIONS OFTHE SLURRY RESULTING FROM STEP (D), F. DIGESTING THE SOLID PORTIONRESULTING FROM STEP (E) WITH AN AQUEOUS MIXTURE OF ALKALI METALHYDROXIDES AT A CONCENTRATION AND AT A TEMPERATURE SUFFICIENT TO EXTRACTTHE ALUMINUM CONTENT FROM SAID SOLID PORTION,
 2. The method of claim 1in which Step (a), Step (b) and Step (c) are carried out at atemperature of from about 400*C to about 850*C for a time of from aboutone-half minute to about six hours for each step.
 3. The method of claim1 in which Step (a), Step (b) and Step (c) are carried out at atemperature of from about 500*C to about 650*C for a time of from aboutone-half minute to about six hours for each step.
 4. The method of claim1 wherein the reducing atmosphere of Step (b) is selected from the groupconsisting hydrogen, hydrocarbons, carbon monoxide and mixtures thereof.5. The method of claim 1 wherein the oxidizing atmosphere of Step (c) isselected from the group consisting of air, oxygen and mixtures thereof.6. The method of claim 1 wherein the solvent of Step (d) is selectedfrom the group consisting of water and alkaline solutions.
 7. The methodof claim 1 wherein the alkali metal hydroxides of Step (f) are selectedfrom the group consisting of sodium hydroxide and potassium hydroxide.8. The method of claim 1 in which the precipitation of silica of Step(h) is carried out by heating the liquid to a temperature of about 90*Cfor at least one hour at atmospheric pressure.
 9. The method of claim 1in which the precipitation of silica of Step (h) is carried out byheating the liquid at a pressure of from about 0.5 atmospheres to about7 atmospheres at a temperature of from about 90*C to about 200*C for atleast fifteen minutes.
 10. The method of claim 1 in which theprecipitation of silica of Step (h) is accelerated by seeding withsodium aluminum silicates.
 11. The method of claim 1 in which theprecipitation of aluminum hydroxide of Step (j) is carried out bycooling the liquid until crystalline aluminum hydroxide is formed. 12.The method of claim 1 in which the precipitation of aluminum hydroxideof Step (j) is accelerated by seeding with aluminum hydroxide crystals.13. The method of claim 1 containing the additional step ofprecipitating potassium sulfate from the liquid resulting from Step (e).14. The method of claim 1 containing the additional step of convertingthe sulfate removed in Step (b) into sulfuric acid.
 15. The method ofclaim 1 containing the additional step of converting the sulfate removedin Step (b) into elemental sulfur.